Fixed drawing a 1px high polygon

Tests/test_imagedraw.py

@@ -531,6 +531,20 @@ def test_polygon_kite():
         assert_image_equal(im, Image.open(expected))
 
 
+def test_polygon_1px_high():
+    # Test drawing a 1px high polygon
+    # Arrange
+    im = Image.new("RGB", (3, 3))
+    draw = ImageDraw.Draw(im)
+    expected = "Tests/images/imagedraw_polygon_1px_high.png"
+
+    # Act
+    draw.polygon([(0, 1), (0, 1), (2, 1), (2, 1)], "#f00")
+
+    # Assert
+    assert_image_equal(im, Image.open(expected))
+
+
 def helper_rectangle(bbox):
     # Arrange
     im = Image.new("RGB", (W, H))

src/libImaging/Draw.c

@@ -489,15 +489,15 @@ polygon_generic(Imaging im, int n, Edge *e, int ink, int eofill,
     }
 
     for (i = 0; i < n; i++) {
-        if (e[i].ymin == e[i].ymax) {
-            continue;
-        }
         if (ymin > e[i].ymin) {
             ymin = e[i].ymin;
         }
         if (ymax < e[i].ymax) {
             ymax = e[i].ymax;
         }
+        if (e[i].ymin == e[i].ymax) {
+            continue;
+        }
         edge_table[edge_count++] = (e + i);
     }
     if (ymin < 0) {